The invention relates to a vacuum brake booster, having a vacuum chamber and a working chamber separated from one another by a movable wall, and a control valve which comprises a control valve housing coupled workingly to the movable wall and which, for achieving a pressure difference at the movable wall, is capable of controlling the supply of atmospheric pressure or above-atmospheric pressure to the working chamber in dependence upon the displacement of an input element of the vacuum brake booster, wherein the control valve housing comprises an outer sleeve and an inner sleeve, which is disposed radially at the inside of and coaxially with the outer sleeve and is connected by a plurality of webs to the outer sleeve.
Such a vacuum brake booster in tandem-design is known from DE-OS 24 36 144, and corresponding U.S. Pat. No. 3,897,718 which is incorporated by reference herein. In accordance with the tandem design, a housing of the vacuum brake booster is divided by stationary walls into two separate housing portions each of a fixed volume. Each of said two separate housing portions is subdivided by a movable wall into a vacuum chamber and a working chamber. Altogether, the vacuum brake booster known from DE-OS 24 36 144 comprises two movable walls, which are disposed inside the housing of the vacuum brake booster and coupled rigidly to a control valve housing.
Given a movement of the control valve housing relative to the housing of the vacuum brake booster, vacuum-tight guidance of the control valve housing has to be guaranteed. For said reason, an outer sleeve of the control valve housing has radially at the outside two axially offset sliding surfaces, on each of which a ring seal sealing a stationary wall in the direction of the control valve housing slides.
The outer sleeve is connected by a plurality of webs to an inner sleeve so as to produce an air flow path between outer sleeve and inner sleeve. The inner sleeve functions as a guide for an actuating piston, which is coupled to the input element of the vacuum brake booster and cooperates via a cylindrical sensing element with an elastomer reaction disk. The actuating forces, which the actuating piston introduces into the reaction disk by means of the sensing element and which are summoned up by the driver, are transmitted from the reaction disk to a reaction piston. Besides the actuating forces, the booster forces attributable to the displacement of the movable walls coupled to the control valve housing are additionally introduced into the reaction disk by means of an end face coupled to the inner sleeve. The booster forces are transmitted from the outer sleeve of the control valve housing by means of the plurality of webs to the inner sleeve.